The present invention is directed to a device for removing noise from a power supply. More particularly the present invention is directed to a device for removing noise from a power supply before it reaches a clock generator.
Continuing developments in the semiconductor field have allowed circuit elements to shrink smaller and smaller. One result of this is that the particular circuit elements are in closer and closer proximity. While this is generally advantageous in that the elements require less power, less cooling and less space, sometimes deleterious effects also occur. One particular result of placing elements in close proximity is that noise is more easily carried from one section of a device to another.
One particular place where this occurs is in the voltage regulator section of the voltage source on a motherboard of a processor platform. Switching regulator noise is often generated in this section. This noise may be carried through the power plane or ground plane to other circuits which are mounted on the motherboard. In particular, the clock chip phase lock loop circuit is susceptible to this type of noise. Since higher frequencies are now involved, the switching noise is also of higher frequency and accordingly is more likely to cause problems than in the past. If switching noise at about 150 KHz enters the clock chip, the clocks may start drifting up to 3% of their nominal frequency. This can affect the signal quality and jitter resulting in a functional failure. Traditional decoupling capacitors can reduce some of the noise. However, if insufficient numbers of capacitors are provided, the clock is susceptible to drift. Further, as the switching circuits get closer to the clock chip, the effect will increase, resulting in more failures. While increasing the number of decoupling capacitors around the clock generator and voltage regulator section will help to reduce the noise, it will increase the cost and size of the motherboard.
FIG. 1 shows the basic arrangement 10 of a circuit having a voltage source 12 and a clock circuit 14. The voltage source provides a voltage input 16 to the clock. The clock then generates output clock signals. Both the voltage source and the clock are grounded. Noise can travel either through the grounding connection or through the voltage connection.